1. Field of the Invention
The present invention relates to an insulation structure for insulating between electrodes and between cells of a bipolar battery using a polymer electrolyte.
2. Description of the Related Art
In recent years, lithium ion secondary batteries which can attain high energy and power densities have been developed as large capacity power sources of electric vehicles and the like. These lithium ion secondary batteries have a basic construction as follows. A positive electrode is made of an aluminum collector to which a positive electrode active material such as lithium cobaltate and a conductive material such as acetylene black are applied using a binder. A negative electrode is made of a copper collector to which carbon particles are applied using a binder. The positive and negative electrodes are placed together with a porous polyolefin film between them as a separator and are immersed in a non-aqueous electrolytic solution containing LiPF6 or the like. When applying this kind of lithium ion secondary batteries to an electric vehicle or the like, batteries having the same construction are serially connected to construct a battery module unit. Further, an assembled battery is constructed by serially connecting these battery module units.
In view of energy and power densities of a battery, there have been demands for improved connections between cells and between modules in terms of connection resistance, space, and weight. Recently, a battery has been proposed in which a bipolar electrode unit is employed. In this bipolar electrode unit, the resistance of a connection between cells can be reduced, and therefore downsizing thereof is expected to be realized (refer to Japanese Patent Application Laid-Open No. H8-7926). In this proposal, a so-called cladding material is used, which is made by rolling two types of metal foils on a collector. Further, an electrolyte used in this proposal is liquid. Therefore, a hermetic seal is inevitable for each cell unit, and it is possible that liquid junction occurs between the cells.
When a solid polymer electrolyte is used instead of the liquid electrolyte, the hermetic seal is not required, and thereby a practical bipolar battery can be constructed. A conventional example of a bipolar battery having a structure corresponding to this structure is shown in FIGS. 1A and 1B (refer to Unexamined Utility Model Application Publication No. H4-54148). This bipolar battery is made of an electrode stacked body 9 which is constructed by stacking a plurality of bipolar electrodes (electrode layers) 8 sandwiching a polymer electrolyte layer 4 therebetween. Each of the bipolar electrodes 8 includes a positive electrode layer 2 on one side of a collecting foil 1, and a negative electrode layer 3 on the other side of the same. The electrodes of the uppermost and lowermost layers do not have the bipolar electrode structure but have a structure in which only the necessary electrode layer is formed on one side of the collector (not shown). In the structure of the bipolar battery, single cells 10 are serially connected.